Process for preparing bicomponent fibers comprising poly(trimethylene terephthalate)

ABSTRACT

Disclosed is a process for preparing crimpable bicomponent fibers from two poly(trimethylene terephthalate) starting materials that differ from one another in intrinsic viscosity. One starting material is characterized by an intrinsic viscosity ≦0.7 dL/g. The relatively low intrinsic viscosity allows the employment of a low melt temperature, with concomitant reduction in the evolution of acrolein, and without significant degradation in the properties or processibility of the bicomponent fiber.

FIELD OF THE INVENTION

This invention pertains to a melt spinning process for the production of bicomponent fibers comprising poly(trimethylene terephthalate).

BACKGROUND OF THE INVENTION

Melt spun bicomponent fibers are well-known in the art. They find particular utility in the art for forming fibers and yarns of particularly high bulk. Bicomponent fibers are formed when two or more melt streams comprising differing polymers are combined in the spinneret to form a single fiber. Crimped fibers can be prepared from bicomponent fibers having side by side or eccentric sheath/core structures when the two polymers making up the two components differ in shrinkage properties. When the as-spun bicomponent fiber is treated to develop the shrinkage of the fibers, typically by heat treatment, the different degrees of shrinkage cause the fibers to take a helical shape thereby developing a crimped configuration. The polymers making up the two components can be chemically distinct, such as a bicomponent fiber whereof one component is poly(ethylene terephthalate) and the other component is poly(trimethylene terephthalate) (PTT). Alternatively, the two components can be chemically the same, but differ in physical properties related to shrinkage.

Chang et al. U.S. Pat. No. 7,147,815 discloses a side-by-side or eccentric sheath-core bicomponent fiber comprising a first fiber component comprising a first composition comprising a first poly(trimethylene terephthalate) (PTT); and a second fiber component comprising a second composition comprising a second PTT wherein said first and second PTT differ from one another in intrinsic viscosity by 0.03 to 0.5 dL/g. Chang employs PTT starting materials characterized by IV in the range of 0.86 to 1.01 dL/g. Chang teaches the employment of melt temperatures up to 270° C. to effect a reduction in IV of the 0.86 dL/g starting material to as low as 0.70 dL/g in the melt stream of one component in order to effect high crimp contraction.

Yoshimura et al. JP 2000256918A, discloses sheath-core or side-by-side bicomponent fibers wherein one side (A) comprises at least 85 mole % poly(trimethylene terephthalate) and the other side comprises (B) at least 85 mole % poly(trimethylene₃₀terephthalate) copolymerized with 0.05-0.20 mole % of a tri-functional comonomer; or the other side comprises (C) at least 85 mole % poly(trimethylene terephthalate) not copolymerized with a tri-functional comonomer wherein the inherent viscosity of (C) is 0.15 to 0.30 less than that of (A).

SUMMARY OF THE INVENTION

In one aspect, the invention provides a bicomponent fiber is consisting essentially of a first poly(trimethylene terephthalate) fiber component and a second poly(trimethylene terephthalate) fiber component wherein said bicomponent fiber is characterized by a molecular weight distribution that exhibits a polydispersity index >2.2 and an intrinsic viscosity in the range of of 0.72 to 0.84 and wherein said first fiber component and said second fiber component are disposed with respect to one another in said bicomponent fiber in a configuration suitable for the development of crimp.

The invention further provides a process for preparing a bicomponent fiber comprising melting a first poly(trimethylene terephthalate) starting material characterized by an intrinsic viscosity of ≦0.7 dL/g to form a first melt stream characterized by a melt temperature less than 250° C., said first melt stream being characterized by an intrinsic viscosity that is no more than 0.03 dL/g lower than the intrinsic viscosity of said first starting material; melting a second poly(trimethylene terephthalate) starting material characterized by an intrinsic viscosity >0.7 dL/g to form a second melt stream, with the proviso that the difference between the intrinsic viscosity of said first and second melt streams is >0.1 dL/g; providing said first and second melt streams to a spinneret therein contacting said first melt stream with said second melt stream; extruding a molten fiber from said spinneret; and, quenching said molten fiber to form a solid bicomponent fiber characterized by a first component and a second component disposed with respect to one another in a configuration suitable for the formation of crimp.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a bicomponent fiber spinning configuration suitable for the process of the invention.

FIG. 2 is a schematic representation of an apparatus suitable for use in drawing, annealing, and winding the bicomponent fiber produced in the process of the invention.

FIG. 3 is a schematic representation of a resin melting and feeding system suitable for use in the process of the invention.

DETAILED DESCRIPTION

When a range of values is provided herein, it is intended to encompass the end-points of the range unless specifically stated otherwise. Numerical values used herein have the precision of the number of significant figures provided, following the standard protocol in chemistry for significant figures as outlined in ASTM E29-08 Section 6. For example, the number 40 encompasses a range from 35.0 to 44.9, whereas the number 40.0 encompasses a range from 39.50 to 40.49.

As used herein, “bicomponent fiber” means a fiber comprising a pair of polymers adhered to each other along the length of the fiber, so that the fiber cross-section is for example a side-by-side, eccentric sheath-core or other suitable cross-sections from which useful crimp can be developed.

In the absence of an indication to the contrary, a reference to “poly(trimethylene terephthalate)” (PTT), is meant to encompass homopolymers and copolymers containing at least 70 mole % trimethylene terephthalate repeat units.

PTT is prepared by the polycondensation of dimethyl terephthalate, or the corresponding diacid, with 1,3-propanediol. Suitable copolyesters can be prepared by adding a third reactant to the polymerization reaction. The third ingredient can be an additional diester or diacid, or an additional glycol. The comonomer typically is present in the copolyester at a level in the range of about 0.5 to about 15 mole %, and can be present in amounts up to 30 mole %. Preferably the PTT is a homopolymer.

Suitable PTT can contain minor amounts of other comonomers, and such comonomers are usually selected so that they do not have a significant adverse effect on properties. Such other comonomers include 5-sodium-sulfoisophthalate, for example, at a level in the range of about 0.2 to 5 mol-%. Very small amounts of trifunctional comonomers, for example trimellitic acid, can be incorporated for viscosity control.

Molecular weight of the PTT can be determined by any of a variety of methods. One such method commonly employed in the art of polyester polymers is the measurement of so-called intrinsic viscosity (IV). The IV of a polymer is determined by extrapolation of the measured solution viscosity of the polymer to zero concentration of polymer. The intrinsic viscosity so determined can then be related to the weight-average molecular weight (M_(w)) of the polymer by the Mark-Houwink equation, as described in Polymer Chemistry, 5^(th) ed., by Charles E. Carrahar, Marcel Dekker (2000). There is some inconsistency in the art regarding the designation “IV” for solution viscosity of a polymer. In some instances in the art “IV” is taken to indicate so-called “inherent viscosity” which is related to but not equivalent to intrinsic viscosity. For the purposes of the present invention, the abbreviation “IV” will always refer to intrinsic viscosity.

Another method for determining molecular weight is by so called size-exclusion chromatography (SEC). A suitable method for performing SEC on the polymers of the invention is provided infra. SEC has the advantage of defining the entire molecular weight distribution, whereas intrinsic viscosity defines a single point on that distribution. The ratio of the weight average molecular weight (M_(w)) to the number average molecular weight (M_(n)) is known as the polydispersity index (PDI) of the polymer, and is an indicator of the breadth of the molecular weight distribution. Polycondensation reactions, such as those employed in the preparation of PTT, are known to exhibit PDIs of about 2.0±0.1.

The inherent error in the determination of the molecular weights recited herein, either by SEC or by IV, was about 3%.

In one aspect, the present invention provides a bicomponent fiber comprising a first poly(trimethylene terephthalate) fiber component and a second poly(trimethylene terephthalate) fiber component wherein said bicomponent fiber is characterized by a molecular weight distribution that exhibits a polydispersity index >2.2 and an intrinsic viscosity in the range of of 0.72 to 0.84 and wherein said first fiber component and said second fiber component are disposed with respect to one another in said bicomponent fiber in a configuration suitable for the development of crimp.

The molecular weight, as indicated either by the distribution provided by SEC, or by the value of IV, of the bicomponent fiber hereof is not predictable strictly by considering the molecular weights of the starting materials. It is known in the art that the molecular weight of PTT will undergo thermally induced reduction. The extent of that reduction will depend upon the starting molecular weight, the temperature of the melt, the residence time at that temperature, the presence of heat stabilizers, among other factors. However, certain characteristics are peculiar to bicomponent fibers.

The bicomponent fibers hereof are prepared in a process in which the molecular weights of the two components differ, but not by so much that analysis by SEC describes two distinct populations. In the experiments described infra, a single molecular weight distribution curve was observed, but the width of the curve was greater than would be observed from a single condensation polymer; that is, the PDI was greater than 2.2.

Similarly, the IV of the starting materials was not fully determinative of the IV of the spun bicomponent fibers. Experiments have shown that the IV of the starting material characterized by IV≦0.7 dL/g, processed in the temperature range of 240-250° C. according to the process hereof, underwent no more than 4% reduction because the relatively low molecular weight PTT could be processed at an unusually low temperature.

Consequently, the bicomponent fiber hereof bears one component with an unusually low IV that causes the IV of the entire bicomponent fiber to be unusually low, namely in the range of 0.72 to 0.84.

In one embodiment of the bicomponent fiber hereof, the said first fiber component and said second fiber component are disposed with respect to one another in said bicomponent fiber in a side by side configuration.

In an alternative embodiment, said first fiber component and said second fiber component are disposed with respect to one another in said bicomponent fiber in an eccentric sheath/core configuration.

In one embodiment, the bicomponent fiber is a staple fiber. In a further embodiment, the staple fiber has a length of 0.5 to 6 inches.

In one embodiment, the bicomponent fiber is crimped.

In one embodiment, a plurality of bicomponent fibers hereof are interlaced or otherwise entangled with one another in the form of a yarn.

In one embodiment, the bicomponent fiber exhibits orientation. Fiber orientation can be determined by measuring the birefringence of the fiber, a methodology well-known in the art. The higher the birefringence of the fiber, the greater degree of orientation.

In another aspect, the invention provides a process for preparing a bicomponent fiber comprising melting a first poly(trimethylene terephthalate) starting material characterized by an intrinsic viscosity of ≦0.7 dL/g to form a first melt stream characterized by a melt temperature less than 250° C., said first melt stream being characterized by an intrinsic viscosity that is no more than 0.03 dL/g lower than the intrinsic viscosity of said first starting material; melting a second poly(trimethylene terephthalate) starting material characterized by an intrinsic viscosity >0.7 dl/g to form a second melt stream, with the proviso that the intrinsic viscosity difference between said first and second melt streams is >0.1 dL/g; providing said first and second melt streams to a spinneret therein contacting said first melt stream with said second melt stream; extruding a molten fiber from said spinneret; and, quenching said molten fiber to form a solid bicomponent fiber characterized by a first component and a second component disposed with respect to one another in a configuration suitable for the formation of crimp.

In one embodiment of the process hereof, the first component and the second component are disposed with respect to one another in a side by side configuration.

In an alternative embodiment of the process hereof, the first component and the second component are disposed with respect to one another in an eccentric sheath/core configuration.

n one embodiment of the process hereof, the first starting material is characterized by an IV in the range of 0.60 to 0.68.

In one embodiment, the second starting material is characterized by an IV>0.8 dL/g. In a further embodiment, the second starting material is characterized by an IV>0.9 dL/g.

In one embodiment of the process hereof, the first melt stream is at a temperature in the range of 240 to 245° C.

In one embodiment of the process hereof, the intrinsic viscosity difference between said first and second melt streams is >0.2 dL/g.

According to the process of the invention, a first starting material, typically commercially available ⅛″ pellets, is characterized by an IV 0.7. The lower limit to the IV of a suitable first starting material depends upon the specific circumstances of the fiber spinning process such as the denier of the fiber, the proportion of the two components, the temperature of the low IV component, and so forth. The lower IV limit has been crossed when the lower IV component undergoes breakage or cracking during spinning, post processing, or in ordinary use.

Suitable poly(trimethylene terephthalate) is available from E. I. du Pont de Nemours and Company, Wilmington, Del., under the trademark Sorona®.

During fiber spinning, the PTT in the molten phase undergoes high shear forces in the spinneret that form the fiber, followed by further high shear as the fiber is drawn during quenching. The polymer must be of sufficiently high molecular weight to allow retention of mechanical integrity during these stressful treatments. For these reasons, PTT fiber, including bicomponent fiber, is generally formed from PTT starting material characterized by an IV of 0.86 or higher, as taught in Chang et al., op.cit.

It is known in the art that melt processing of PTT can result in the production of acrolein (C₃H₄O-prop-2-enal), a noxious by-product. Experiments have been performed to determine the affect of processing temperature upon the production rate of acrolein. Results show that for a residence time of 5 minutes, the amount of acrolein produced from a PTT melt increased by a factor of 10 when the temperature was raised from ca. 240° C. to ca. 280° C.

It has been found in the practice of the process of the present invention that bicomponent fiber having good physical properties could be prepared when the starting material of one of the components was characterized by an IV≦0.7 dL/g. Moreover, it was found that the starting material characterized by the relatively low IV of ≦0.7 dL/g can be melted and processed at a melt temperature in the range of 240-250° C., preferably 240-245° C., and spun smoothly and controllably into one component of the bicomponent fiber hereof. Higher IV starting material, such as that disclosed in Chang at al., op. cit., cannot be stably spun into fiber at temperatures in the range of 240-250° C.

The low IV component of Chang et al., op.cit., is achieved by subjecting a much higher IV polymer to 270° C. a temperature sufficiently high to cause significant polymer degradation to much lower IV, with concomitant high evolution of acrolein. The resulting PTT is unusually high in carboxylate end groups with respect to the low IV starting material of the present invention.

The low melt temperature characteristic of the process hereof imparts several benefits, including a) the IV remains substantially unchanged in processing because of the low temperature, providing improved process control; b) the production of acrolein is greatly reduced vis a vis processes requiring one component to be heated to ca. 270° C. in order to achieve sufficiently low IV for the lower IV component, as well as other improvements in processibility that may result from the lower molecular weight.

FIG. 1 is a schematic of the extruders, pump blocks and spin block that make up a suitable bicomponent fiber spinning machine extrusion system. The spinning machine comprises two polymer extrusion systems denoted W for the “West” system and E for the “East” system. No significance attached to the geographic designation “East” and “West.” It is simply a convention adopted to distinguish between two otherwise nearly identical systems. In FIG. 1, Ktron KCLK720 weight loss feeders (1W/1E) feed polymer pellets into Werner and Pfleiderer co-rotating 28 mm twin screw extruders (2W/2E). The melt streams so formed are fed to the pump blocks (4W/4E). Each pump block provided with an associated ballast pump (3W/3E) and metering pump (5W/5E). The ballast pump is used to direct part (or the entire) melt stream to waste while the remainder of the melt stream is processed through the metering pump. The ballast pumps are 1.32 cc/rev Zenith gear pumps. The respective metering pump speeds are adjusted to provide greater or lesser throughput rates. By adjusting the relative pump speeds in the East and West extruders, the relative concentration of the respective polymer components in the spun fiber can be adjusted. The West meter pump (5W) is a 3.30 cc/rev Zenith gear pump. The East meter pump (5E) is a 1.98 cc/rev Zenith gear pump. The two melt streams are fed from the respective metering pumps to converge inside a single spin block, 9, provided with a recess into which a spin pack is fitted, the spin-pack consisting of an annular bicomponent filtration pack 10 and a spinneret, 11. In the Examples infra, the filtration pack 10 consisted of one 50 mesh filter screen, three 200 mesh filter screens and about 20 milliliters of 10/25 glass chips. The 3.12 inch diameter bicomponent post-coalescence spinneret, 11, comprised 34 pairs of holes (not shown) arranged in two circular arrays. Each hole was 0.63 mm in diameter by 4.24 mm in length. Thermocouples placed at the exit of the extruders (7W/7E) were used to determine the melt stream temperatures in the Examples. The temperature of the melt streams in the pump blocks (6W/6E) and spin block can be optimized to control pack pressure.

FIG. 2 illustrates a crossflow melt-spinning apparatus which is suitable for use in the process of the invention. Quench gas 21 enters zone 22 below spinneret face 11 through plenum 24, past hinged baffle 28 and through screens 25, resulting in a substantially laminar gas flow across the still-molten fibers 26 exiting the spinneret. Baffle 28 is hinged at the top, so that its position can be adjusted to change the flow of quench gas across zone 22. Spinneret face 11 is recessed above the top of zone 22 by distance A, so that the quench gas does not contact the just-spun fibers until after a delay during which the fibers could be heated by the sides of the recess. In the Examples infra, the thus quenched fibers were transferred from the spinning floor to the roll array on the floor below (see FIG. 3) via baffle 27. Finish was applied to the now-solid fibers by contacting with finish roll 210.

In FIG. 3, fiber 26, is directed from the finish roll around driven roll 31, around idler roll 32, and then around heated rolls 33. The temperature of rolls 33 can be in the range of about 50° C. to about 70° C. The fiber is then passed to heated draw rolls 34. The temperature of rolls 34 can be in the range of about 50° C. to about 170° C., preferably about 100° C. to about 120° C. From rolls 34, the fiber is then transferred to heated rolls 35, passed around optional unheated rolls 36 (which adjust the yarn tension for satisfactory winding), and then to windup 37. The draw ratio (the speed of 34 divided by the speed of 33) is in the range of about 1.4 to about 4.5, preferably about 3.0 to about 4.0. No significant tension (beyond that necessary to keep the fiber on the rolls) need be applied between the pair of rolls 33 or between the pair of rolls 34. Heat treating can also be carried out with one or more other heated rolls, steam jets or a heating chamber such as a “hot chest”. The heat-treatment can be carried out at substantially constant length, for example, by rolls 35 in FIG. 3, which heat the fiber to a temperature in the range of about 110° C. to about 170° C., preferably about 120° C. to about 160° C.

The duration of the heat-treatment is dependent on yarn denier; what is important is that the fiber can reach substantially the same temperature as that of the rolls. If the heat-treating temperature is too low, crimp can be reduced under tension at elevated temperatures, and shrinkage can be increased. If the heat-treating temperature is too high, operability of the process becomes difficult because of frequent fiber breaks. It is preferred that the speeds of the heat-treating rolls and draw rolls be substantially equal in order to keep fiber tension substantially constant at this point in the process and thereby avoid loss of fiber crimp.

Alternatively, the feed rolls can be unheated, and drawing can be accomplished by a draw-jet and heated draw rolls which also heat-treat the fiber.

An interlace jet optionally can be positioned between the draw/heat-treat rolls and windup.

Finally, the fiber is wound up. A typical wind up speed in the manufacture of the products of the present invention is about 2,500 meters per minute (mpm). The range of usable wind up speeds is about 2,000 mpm to 6,000 mpm.

EXAMPLES Test Methods Measurement of Crimp Contraction

Each fiber was formed into a skein of about 5000 +/−5 total denier (5550 dtex) with a skein reel at a tension of about 0.1 gpd (0.09 dN/tex). The skein was then halved in length by folding the skein in two in order to accommodate the interior of the oven used for heatsetting. The folded skein was hung at its mid-section from a hook and was conditioned at 70 +/−1° F. (21 +/−1° C.) and 65 +/−2% relative humidity for a minimum of 16 hours. The folded skein was then hung substantially vertically on a rack from a hook at its mid-section and a 1.5 mg/den (1.35 mg/dtex) weight was hung through the two loops of the folded skein at the bottom of the skein. The weighted skein was then heated in an oven for 5 min at 250° F. (121° C.) after which the rack and skein were removed and allowed to cool for 5 minutes, then conditioned at 70° F. +/−1° F. (21 +/−1° C.) and 65% +/−2% relative humidity for a minimum of 2 hours with the 1.5 mg/den weight left on the skein for the remainder of the test. The length of the skein was measured to within 1 mm and recorded as “Ca”. Next, a 1000 gram weight was hung from the bottom of the skein, allowed to reach equilibrium and the length of the skein measured within 1 mm and recorded as “La”. Crimp contraction “CCa” value (%) was calculated according to the formula:

CCa=100×(La-Ca)/La

Determination of IV

Intrinsic Viscosity (IV) was determined using the Goodyear R-103b method.

Determination of Molecular Weight Distribution

Molecular weight distribution was determined employing Size Exclusion Chromatography (SEC), a technique well-known in the art for use in determining the molecular weight distribution of polyesters. The polydispersity index (PDI) was determined as PDI=M_(w)/M_(n), wherein M_(w) is the weight average molecular weight, and M_(n) is the number average molecular weight, as determined from SEC.

Fiber Preparation

Three grades of Sorona® Poly (trimethylene terephthalate) resin pellets were obtained from E.I DuPont de Nemours and Company, Wilmington, Del. One grade was characterized by an IV of 1.02 dL/g, a second by an IV of 0.96 dL/g, and a third by an IV of 0.66 dL/g. In preparation for melt spinning, each grade was dried under nitrogen in a vacuum oven for 15 hours at 25 inches mercury vacuum and a temperature of 120° C. The thus dried resin pellets were transferred directly to the nitrogen-purged feed hopper of the spinning machine, FIG. 1.

The melt spun bicomponent filament was air quenched. Referring to FIG. 1, the quench air 1 was supplied at room temperature and impinged on the extruded thread line 6 at 0.12 m/sec as measured 0.61 meters below the spinneret.

Comparative Example A

1.02 IV Sorona® pellets were fed after drying to both extruders described supra. Both extruders were set up identically with the heating profile in the nine zones of 180/240/250/250/255/255/250/255/255° C. The temperature of the melt stream measured at the exit of the extruder was 256° C.

Both East and West metering pump (5W5E in FIG. 1) speeds were set at 14.4 g/min The speeds of both ballast pumps were set at 6.6 g/min. Referring to FIG. 3, the thread line was wrapped six times around the unheated feed roll/separator roll 31/32 which was operated at a linear speed of 796 m/min. The thread line was then wrapped five times around the 65° C. draw rolls 33 which was also operated at a linear speed of 796 m/min. The thread line was then wrapped nine times around annealing rolls 34 operated at 150° C. and a linear speed of 2550 m/min. The thread line was then wrapped nine times around the unheated letdown rolls 35 operated at a linear speed of 2550 m/min. The thread line was then wrapped six times around an additional set of unheated letdown rolls 36 operated at a linear speed of 2550 m/min. The yarn was collected at a Barmag SW6 2s 600 winder (Barmag AG, Germany) 37 at a linear rate of 2480 m/min on a cardboard tube.

Table 1 shows the results for the fibers made in Comparative Example A (CE A) using the method described in the Fiber Preparation section. The properties of the fiber prepared from the two identical melt streams are shown in Table 1. Also shown in Table 1 are the properties of a fiber formed from a single melt stream (CE), run at the same rate as described for one component of the two component fiber. The term “n/a” means “not applicable.”

Both IV and molecular weight distribution were determined for the as spun fibers in question. Crimp contraction, CCa, was also measured. Very low values of CCa were obtained for this comparative example.

TABLE 1 Starting Melt Stream Material IV IV* (dL/g) (dL/g) Bicomponent Draw CCa West East West East Fiber IV (dL/g) Ratio (%) PDI Denier Bicomponent fiber 1.02 1.02 n/a n/a 0.94 3.20 1.10 2.12 113 CE A Monocomponent 1.02 n/a 0.90 n/a n/a n/a n/a 2.09 n/a Fiber CE A-1

Examples 1-3

The 1.02 IV Sorona® resin pellets were again fed to the West extruder, as in CE A. However, the East extruder was fed with the 0.66 IV Sorona® resin pellets. The temperature profile of the 9 heating zones of s the East extruder was set to 140/200/235/245/245/245/245/245/245° C. The temperature of the melt stream measured at the exit of the extruder was 245° C.

The 3.0 draw ratio item was run with a feed roll and draw roll rotating at 850 m/min. The 3.2 draw ratio item was collected with a feed roll and draw roll rotating at 796 m/min. The 3.4 draw ratio item was collected with a feed roll and draw roll rotating at 750 m/min. All other roll speeds and temperatures remained the same as in Comparative Example 1.

The results for the fibers made in Examples 1-3 are shown in Table 2.

Also shown in Table 2 are the properties of a fiber formed from each melt stream separately (Ex 1-1 and Ex 1-2), run at the same rate as described for each component of the two component fiber. The extrudates so produced were co-dissolved in trichloroethane and analyzed by SEC.

20

CL5517 WO PCT

TABLE 2 Melt Stream Chip IV IV* Bicomponent Draw West East West East Fiber IV Ratio Cca, % PDI Denier Example 1 1.02 0.66 n/a n/a 0.79 3.0 41.7 2.28 110 Example 2 1.02 0.66 n/a n/a 0.80 3.2 36.8 2.33 110 Example 3 1.02 0.66 n/a n/a 0.79 3.4 35.7 2.32 111 Monocomponent 1.02 n/a 0.90 n/a n/a n/a n/a 2.09 n/a Fiber Ex 1-1 Monocomponent n/a 0.66 n/a 0.63 n/a n/a n/a 2.11 n/a Fiber Ex 1-2 50/50 weight % n/a n/a 0.90 0.63 n/a n/a n/a 2.31 n/a Mixture of Ex 1- 1 and Ex 1-2

Example 4

The conditions of Example 3 were replicated except that the starting material for the West extruder was characterized by an IV of 0.96, and the extruder profile was 180/255/255/255/255/255/255/255/255° C. The transfer line temperature for the melt stream from the West extruder was 256° C. Also shown in Table 3 are the properties of a fiber formed from each melt stream separately (Ex 4-1 and Ex 4-2), run at the same rate as described for each component of the two component fiber. The extrudates so produced were co-dissolved in trichloroethane and analyzed by SEC.

The results for the fibers made in Example 4 are shown in Table 3.

TABLE 3 Starting Material Fiber IV Bicomponent Draw West East West East Fiber IV Ratio Cca PDI Denier Example 4 0.96 0.66 n/a n/a 0.78 3.4 12.0 2.28 111 Monocomponent 0.96 n/a 0.81 n/a n/a n/a n/a 2.16 n/a Fiber Ex 4-1 Monocomponent n/a 0.66 n/a 0.63 n/a n/a n/a 2.11 n/a Fiber Ex 4-2 50/50 wt-% co- n/a n/a 0.81 0.63 n/a n/a n/a 2.26 n/a solution of Ex 4- 1 and Ex 4-2

Examples 5-7

Example 1 was reproduced, except that the pumping rates of the metering pumps were altered, as shown in Table 4. The results for the fibers made in Examples 5-7 are shown in Table 4.

TABLE 4 Table 4 Starting Pump Speed Polymer Material (g/min) ratio in fiber Fiber IV Draw West East West East (wt-%) (dL/g) Ratio Cca (%) PDI Denier Example 5 1.02 0.66 16.5 16.5 50/50 0.78 3.0 38.6 2.23 128 Example 6 1.02 0.66 20.0 13.5 60/40 0.81 3.0 32.1 2.35 126 Example 7 1.02 0.66 13.5 20.0 40/60 0.75 3.0 27.3 2.30 128 

What is claimed is:
 1. A process comprising melting a first poly(trimethylene terephthalate) starting material characterized by an intrinsic viscosity of ≦0.7 dL/g to form a first melt stream characterized by a melt temperature less than 250° C., said first melt stream being characterized by an intrinsic viscosity that is no more than 0.03 dL/g lower than the intrinsic viscosity of said first starting material; melting a second poly(trimethylene terephthalate) starting material characterized by an intrinsic viscosity >0.7 dL/g to form a second melt stream, with the proviso that the difference between the intrinsic viscosity of said first and second melt streams is >0.1 dL/g; providing said first and second melt streams to a spinneret therein contacting said first melt stream with said second melt stream; extruding a molten fiber from said spinneret; and, quenching said molten fiber to form a solid bicomponent fiber characterized by a first component and a second component disposed with respect to one another in a configuration suitable for the formation of crimp.
 2. The process of claim 1 wherein the first fiber component and the second fiber component are disposed with respect to one another in the bicomponent fiber in a side by side configuration.
 3. The process of claim 1 wherein the first fiber component and the second fiber component are disposed with respect to one another in the bicomponent fiber in an eccentric sheath/core configuration.
 4. The process of claim 1 wherein the first starting material is characterized by an IV in the range of 0.60 to 0.68.
 5. The process of claim 1 wherein the second starting material is characterized by an IV>0.8 dL/g.
 6. The process of claim 5 wherein the second starting material is characterized by an IV>0.9 dL/g.
 7. The process of claim 1 wherein the first melt stream is at a temperature in the range of 240 to 245° C.
 8. The process of claim 1 wherein the difference between the intrinsic viscosity of the first and second melt streams is >0.2 dL/g.
 9. The process of claim 1 wherein the first starting material is characterized by an intrinsic viscosity in the range of 0.60 to 0.68 dL/g, the second starting material is characterized by an intrinsic viscosity >0.8 dL/g, and the difference between the intrinsic viscosity of the first and second melt streams is >0.2 dL/g.
 10. The process of claim 9 wherein the first melt stream is at a temperature in the range of 240 to 245° C.
 11. The process of claim 10 wherein the the second starting material is characterized by an intrinsic viscosity >0.9 dL/g.
 12. The process of claim 1 further comprising subjecting the bicomponent fiber to elevated temperature thereby developing crimp therein. 